全文获取类型
收费全文 | 685篇 |
免费 | 41篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 16篇 |
大气科学 | 87篇 |
地球物理 | 179篇 |
地质学 | 245篇 |
海洋学 | 60篇 |
天文学 | 98篇 |
综合类 | 4篇 |
自然地理 | 39篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 48篇 |
2015年 | 36篇 |
2014年 | 46篇 |
2013年 | 59篇 |
2012年 | 47篇 |
2011年 | 57篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 28篇 |
2007年 | 43篇 |
2006年 | 25篇 |
2005年 | 20篇 |
2004年 | 27篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有728条查询结果,搜索用时 31 毫秒
31.
Spatial distribution of crustaceans associated with shallow soft‐bottom habitats in a coral reef lagoon
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats. 相似文献
32.
Crustacean decapod assemblages associated with fragmented Posidonia oceanica meadows in the Alboran Sea (Western Mediterranean Sea): composition,temporal dynamics and influence of meadow structure
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ángel Mateo‐Ramírez Javier Urra Pablo Marina José L. Rueda José Enrique García Raso 《Marine Ecology》2016,37(2):344-358
The decapod assemblage associated with a Posidonia oceanica meadow located near its western limit of biogeographic distribution was studied over an annual cycle. Fauna samples were taken seasonally over a year (five replicates per season) in two sites located 7 km apart, using a non‐destructive sampling method (airlift sampler) for the seagrass. The dominant species of the assemblage, Pisidia longimana, Pilumnus hirtellus and Athanas nitescens, were associated with the protective rhizome stratum, which is mainly used as a nursery. The correlations between decapod assemblage structure and some phenological parameters of the seagrass shoots and wave height were negative or null, which reflects that species associated with the rhizome had a higher importance than those associated with the leaf stratum. The abundance and composition of the decapod assemblage as well as the ecological indexes displayed a seasonality trend with maximum values in summer‐autumn and minimum in winter‐spring, which were related to the seawater temperature and the recruitment periods of the dominant species. The spatial differences found in the structure and dynamics of the assemblages may be due to variations in the recruitment of the dominant species, probably as a result of the influence of local factors (e.g. temperature, currents) and the high dispersal ability of decapods, together with the patchy configuration and the surrounding habitats. The studied meadows are fragmented and are integrated within a mosaic of habitats (Cymodocea nodosa patches, algal meadows, rocky and sandy bottoms), which promotes the movement of individuals and species among them, maintaining a high species richness and evenness. 相似文献
33.
Holger Frey Christian Huggel Yves Bühler Daniel Buis Maria Dulce Burga Walter Choquevilca Felipe Fernandez Javier García Hernández Claudia Giráldez Edwin Loarte Paul Masias Cesar Portocarrero Luis Vicuña Marco Walser 《Landslides》2016,13(6):1493-1507
The town of Santa Teresa (Cusco Region, Peru) has been affected by several large debris-flow events in the recent past, which destroyed parts of the town and resulted in a resettlement of the municipality. Here, we present a risk analysis and a risk management strategy for debris-flows and glacier lake outbursts in the Sacsara catchment. Data scarcity and limited understanding of both physical and social processes impede a full quantitative risk assessment. Therefore, a bottom-up approach is chosen in order to establish an integrated risk management strategy that is robust against uncertainties in the risk analysis. With the Rapid Mass Movement Simulation (RAMMS) model, a reconstruction of a major event from 1998 in the Sacsara catchment is calculated, including a sensitivity analysis for various model parameters. Based on the simulation results, potential future debris-flows scenarios of different magnitudes, including outbursts of two glacier lakes, are modeled for assessing the hazard. For the local communities in the catchment, the hazard assessment is complemented by the analysis of high-resolution satellite imagery and fieldwork. Physical, social, economic, and institutional vulnerability are considered for the vulnerability assessment, and risk is eventually evaluated by crossing the local hazard maps with the vulnerability. Based on this risk analysis, a risk management strategy is developed, consisting of three complementing elements: (i) standardized risk sheets for the communities; (ii) activities with the local population and authorities to increase social and institutional preparedness; and (iii) a simple Early Warning System. By combining scientific, technical, and social aspects, this work is an example of a framework for an integrated risk management strategy in a data scarce, remote mountain catchment in a developing country. 相似文献
34.
José M. García-Ruiz Yasmina Sanjuán Graciela Gil-Romera Penélope González-Sampériz Santiago Beguería José Arnáez Paz Coba-Pérez Amelia Gómez-Villar Javier Álvarez-Martínez Noemí Lana-Renault Estela Pérez-Cardiel Carlos López de Calle 《山地科学学报》2016,13(10):1760-1772
The conversion of subalpine forests into grasslands for pastoral use is a well-knownphenomenon, although for most mountain areas the timing of deforestation has not been determined. The presence of charcoal fragments in soil profiles affected by shallow landsliding enabled us to date the occurrence of fires and the periods of conversion ofsubalpine forest into grasslands in the Urbión Mountains, Iberian Range, Spain. We found that the treeline in the highest parts of the northwestern massifs of the Iberian Range(the Urbión, Demanda, Neila, and Cebollera massifs) is currently between 1500 and 1600 m a.s.l., probably because of pastoral use of the subalpine belt, whereas in the past it would have reached almost the highest divides(at approximately 2100–2200 m a.s.l.). The radiocarbon dates obtained indicate that the transformation of the subalpine belt occurred during the Late Neolithic, Chalcolithic, Bronze Age, Iron Age, and Middle Ages. Forest clearing was probably moderate during fires prior to the Middle Ages, as the small size of the sheep herds and the local character of the markets only required small clearings, and therefore more limited fires. Thus, it is likely that the forest recovered burnt areas in a few decades; this suggests the management of the forest and grasslands following a slash-andburn system. During the Middle and Modern Ages deforestation and grassland expansion affected most of the subalpine belt and coincided with the increasing prevalence of transhumance, as occurred in other mountains in the Iberian Peninsula(particularly the Pyrenees). Although the occurrence of shallow landslides following deforestation between the Neolithic and the Roman Period cannot be ruled out, the most extensive shallow landsliding processes would have occurred from the Middle Ages until recent times. 相似文献
35.
36.
37.
38.
39.
40.
G. Bru J.A. Fernández-Merodo J.C. García-Davalillo G. Herrera J. Fernández 《Landslides》2018,15(2):257-272
This paper presents an advanced 3D numerical methodology to reproduce the kinematics of slow active landslides, more precisely, to reproduce the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. For this purpose, finite element analyses are performed in a large area covering a long time-span (12 years), in order to exhibit different interacting slope movements. First, we perform a stability analysis using the shear strength reduction (SSR) technique with a Mohr-Coulomb failure criteria. It is done in order to compute factors of safety (FS) and to identify two different scenarios, the first one being stable (FS > 1) and the second one being unstable (FS < 1). In the studied test case, the Portalet landslide (Central Spanish Pyrenees), the first scenario corresponds to an initial stable configuration of the slope and the second one to an unstable excavated configuration. Second, taking the first scenario as an initial condition, a time-dependent analysis is performed using a coupled formulation to model solid skeleton and pore fluids interaction, and a simplified ground water model that takes into account daily rainfall intensity. In this case, a viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behavior and the delayed creep deformation due to the excavation. The fluidity parameter is calibrated to reproduce displacements measured by the monitoring systems. Our results demonstrate that 3D analyses are preferable to 2D ones for reproducing in a more realistic way the slide behavior. After calibration, the proposed model is able to simulate successfully short- and medium-term predictions during stages of primary and secondary creep. 相似文献